You can get the key of Eir by completing a specific task. It’s unlocked with the Wormsinger Rune item that is a random drop, and continues with Wormfeeder Rune item that requires you to kill 50 hive enemies. When you finish it, you’ll get a random key as a reward. Another way to get it is to wait for it to drop from a monster during Patrol. Check out detailed guide How to use and collect Wormsinger rune and get the key.
Where to find the Eir chest
When you spawn at Hull Breach, go towards the crashed spaceship. Once you reach it, turn right and go down into the hallway. Keep to the left-hand wall until you see a tunnel – enter it, then turn left into another when you exit. When you’re out of the second tunnel, the chest will be right in front of you.
This helped a lot thank you I would have been lost trying tie find the chest for ages